Caption: Animation of a flight into the inside of a typical human cell, focusing on a single mitochondrion. Mitochondria are cell organelles that produce ATP, the chemical energy currency of cells. The ATP is produced by cellular respiration, using oxygen and the metabolised products of sugars to drive a series of chemical reactions that produces ATP from ADP. These reactions occur on the inner membrane of the mitochondrion, and are represented here by flashes. This animation is available without the label, see clip K005/0842.